A company's AWS environment includes multiple VPCs across several accounts that are connected via a transit gateway. The network team wants to monitor all network traffic between VPCs for security analysis. Which solution is the most scalable and cost-effective?
Scalable and cost-effective.
Why this answer
VPC Flow Logs capture IP traffic metadata (not full packets) and can be centrally published to an S3 bucket across accounts using a central logging account. Querying with Athena is serverless, scales automatically, and incurs cost only for data scanned, making it the most scalable and cost-effective solution for security analysis of inter-VPC traffic.
Exam trap
The trap here is that candidates may over-engineer the solution by choosing Traffic Mirroring or NLB-based packet capture, thinking full packet inspection is needed, when metadata from Flow Logs is sufficient for security analysis and far more cost-effective at scale.
How to eliminate wrong answers
Option A is wrong because Traffic Mirroring copies full packet contents to a central appliance, which incurs high data transfer and processing costs, and requires managing a separate inspection instance that does not scale elastically. Option C is wrong because streaming Flow Logs to CloudWatch Logs in each account creates a decentralized, harder-to-query setup with higher per-log ingestion and storage costs, and lacks a single pane of glass for cross-account analysis. Option D is wrong because placing a Network Load Balancer in each VPC does not inherently capture traffic; packet sniffers require agent installation and cannot capture all traffic without significant performance overhead and architectural complexity.